Looks fungal, early stages of early blight. Would suggest that you go ahead and remove visibly affected foliage first, then spray. Once a leaf is infected, the condition does not reverse.

If conditions are right; wet and hot, yes, it can spread rapidly.

Well, I'm more familiar with late blight which looks quite different. But I do wonder if the early blight diagnosis is correct.

Before you panic, compare with the linked photo at
http://aggie-horticulture.tamu.edu/tomatoproblemsolver/leaves/12a.html

So, how many leaves are affected? If a few, you might want to remove those, then wait and watch.

Here is a link that might be useful: early blight as shown at TAMU

thanks for the help. Probably early blight. Sprayed on Sat.

Sheila

I was under the impression that early blight starts out as small lesions, enlarge, then area around spots may turn yellow. This looks like yellow chlorosis is developing first. Doesn't look like the yellowing that occurs with powdery mildew either. Wonder if it could be nutritional deficiency such as magnesium? (see link below)

Of course , fungicide spraying is covering all your bases if this is fungal or for whatever fungal diseases do develop in near future.

symptoms of Early blight:
"Early Blight (Alternaria solani)
Symptoms: Early blight is first observed in the field as small brownish-black lesions on the older foliage. The spots enlarge rapidly, and by the time they are 1/4 inch in diameter or larger, concentric rings may be distinguished on the dark brownish portion of the spots. The tissue surrounding the spots may become yellow in color, and when spotting is abundant the entire leaf may yellow." (2005 Florida Plant Disease brochure)

Here is a link that might be useful: Magnesium Deficiency

Farkee, thanks for the help. You could be right.

Now, next question is.. How does one improve Mg in their soil??

Is it something that can be fixed with one application? Or does it take time to repair itself.

Is it something I could get from the usual stores? I believe it is.

Thanks again

sheila

Shiela, I believe some people just spray with solution of magnesium (epsom salt) but you should research this a bit or contact your extension office as too much of one thing creates imbalances. Next season I would get a soil test done.

It is very hard to look at a leaf on the internet and really know what is wrong plus you could have multiple problems as foliar diseases are common in alot of places.
Nutrient problems may be corrected with whatever you are fertilizing with normally and unless severe may not need any additional inputs other than whatever you use to fertilize. I don't know where you live--sandy soils do not hold nutrients very well.

commercial sites on epsom salt:

http://epsomsaltcouncil.org/garden_usage_tips.htm
http://www.epsogrow.com/html/epsomsaltlawn&garden.html